The present invention relates to plasma processing modules for the processing of a semiconductor substrate in the manufacture of integrated circuits. More particularly, the present invention relates to downstream, inductively coupled plasma processing modules and methods of using the modules during the processing of the semiconductor substrates.
Semiconductor substrates are typically processed using plasma processing modules to perform various process steps during the manufacture of the semiconductor devices. Generally, these plasma-enhanced processes are well known to those skilled in the art and include various etching processes and stripping processes.
In recent trends, plasma-enhanced processes have been more frequently used to perform resist stripping. Traditionally, the resist stripping or ashing process has been considered a fairly straight forward process. However, due to the small feature size and increased complexity of devices now common in the semiconductor industry, conventional plasma processing modules tend to cause plasma-induced damage to the semiconductor devices during the processing of the semiconductor substrates. To more thoroughly illustrate the problems associated with the use of conventional plasma processing modules, a prior art inductively coupled plasma processing module 100 will be described with reference to FIG. 1.
As illustrated in FIG. 1, plasma processing module 100 includes a plasma chamber 102 formed by chamber walls 104 and dielectric window 106. Plasma processing module 100 includes a feed gas inlet 108 for allowing feed gasses 109 to flow into chamber 102. An exhaust port 110 is also provided for exhausting gases from chamber 102. An inductive source 112, typically taking the form of a coil positioned on dielectric window 106, is used to energize feed gases 109 within chamber 102 and strike a plasma within the chamber. In this example, inductive source 112 is powered by RF power supply 114.
With the above described configuration, the shape of inductive source 112 causes the plasma within chamber 102 to form a plasma having a primary dissociation zone 116. This primary dissociation zone is the region within the chamber that the plasma most efficiently dissociates feed gases 109 (for example O2 and H2O vapor) into neutral non-charged species (for example O, H, and OH). In the case in which inductive source 112 takes the form of a coil attached to dielectric window 106, primary dissociation zone 116 takes the form of a generally donut shaped region located within chamber 102 directly below the coils of inductive source 112.
Still referring to FIG. 1, plasma processing module 100 also includes a liner 118, such as a quartz liner, for protecting the walls of the plasma chamber from the plasma and reducing the recombination of neutral radicals like O or OH. A chuck 120 is positioned in the bottom of chamber 102 and is configured to support a semiconductor substrate 122. As is known in the art, chuck 120 may be heated to improve the efficiency of the process. Plasma processing module 100 also includes a quartz baffle 124 located above substrate 122. Baffle 124 includes a plurality of openings 126 formed through baffle 124 which cause any gases flowing through chamber 102 to be redistributed so that the gases flow more evenly over substrate 122 than would be the case if baffle 124 were not included in module 100.
Although baffle 124 partially shields substrate 122 from direct exposure to the plasma, portions of substrate 122 remain directly exposed to the plasma. This exposure to the substrate to the plasma may cause different types of the plasma-induced damage. For example, in semiconductor substrates having small feature sizes such as 0.25 xcexcm devices, charge damage can occur when electrically charged species from the plasma accumulate non-uniformly on device gates and interconnections. This charge accumulation can lead to large voltage potentials across individual gates or between devices that can cause gate degradation or loss of gate integrity. Device damage has been found to correlate with the charge species dose that the device is exposed to during the process. Therefore, exposing the device directly to charged species produced within the plasma at high concentration (e.g.,  greater than 1011/cm3) for even a short duration of time (e.g., seconds) or moderate concentration (e.g., 109/cm3 to 1010/cm3) for a longer duration (e.g., tens of seconds) can cause significant problems for this type of device. In another example, device damage has been attributed to direct UV radiation exposure from the plasma. In the conventional configuration of an inductively coupled plasma processing module, such as module 100 described above, portions of substrate 122 are directly exposed to UV radiation from the plasma.
Another problem associated with conventional inductively coupled plasma processing modules such as module 100 is that they often provide relatively poor dissociation of the feed gases. In some cases, much of the RF energy is input into ionization at the expense of dissociation of the feed gas. This poor dissociation decreases the efficiency of and therefore increases the time necessary for processing, further contributing to the above described problem of charge damage to devices on the substrate. This poor dissociation is at least in part due to the fact that the feed gases 109 are not forced to flow directly through the primary dissociation zones 116. As mentioned above, primary dissociation zones 116 are the regions within chamber 102 in which the plasma most efficiently dissociates the feed gases.
The present invention provides improved designs for inductively coupled plasma processing modules and methods of using the novel modules to process semiconductor substrates. These designs provide an isolated plasma containment chamber within the module. This isolated plasma containment chamber prevents the semiconductor substrate from being directly exposed to line-of-sight UV radiation produced by the plasma and substantially reduces the concentration of charged species that the semiconductor substrate is exposed to compared to prior art inductively coupled plasma processing modules. Also, the plasma processing modules of the present invention provide a module that improves the dissociation of the feed gases compared to prior art inductively coupled plasma processing modules. This is accomplished by specifically controlling the flow of gases through the module.
As will be described in more detail hereinafter, a plasma processing module and methods of using the plasma processing module to process a substrate are herein disclosed. The plasma processing module of the present invention includes a plasma containment chamber having a feed gas inlet port capable of allowing a feed gas to enter the plasma containment chamber of the plasma processing module during the processing of the substrate. An inductively coupled source is used to energize the feed gas and for striking a plasma within the plasma containment chamber. The specific configuration of the inductively coupled source causes the plasma to be formed such that the plasma includes a primary dissociation zone within the plasma containment chamber. A secondary chamber is separated from the plasma containment chamber by a plasma containment plate or shield. The secondary chamber includes a chuck and an exhaust port. The chuck is configured to support the substrate during the processing of the substrate and the exhaust port is connected to the secondary chamber such that the exhaust port allows gases to be removed from the secondary chamber during the processing of the substrate. A chamber interconnecting port interconnects the plasma containment chamber and the secondary chamber. The chamber interconnecting port allows gases from the plasma containment chamber to flow into the secondary chamber during the processing of the substrate. The chamber interconnecting port is positioned between the plasma containment chamber and the secondary chamber such that, when the substrate is positioned on the chuck in the secondary chamber, there is no substantial direct line-of-sight exposure of the substrate to the primary dissociation zone of the plasma formed in the plasma containment chamber.
In one embodiment, the feed gas inlet port and the chamber interconnecting port are connected to the plasma containment chamber such that the flow of any feed gases fed into the plasma containment chamber through the feed gas inlet port is directed substantially through the primary dissociation zone of the plasma within the plasma containment chamber. In another embodiment, the feed gas inlet port and the chamber interconnecting port are connected to the plasma containment chamber such that the flow of any feed gases fed into the plasma containment chamber through the feed gas inlet port is caused to pass substantially through the primary dissociation zone of the plasma within the plasma containment chamber two times.
Preferably, the secondary chamber further includes a baffle plate having a plurality of openings formed through the baffle plate. The baffle plate is positioned within the secondary chamber above the substrate such that the plurality of openings in the baffle plate cause any gases moving through the secondary chamber and out the exhaust port to flow over the substrate in a more uniformly distributed flow pattern compared to what the flow pattern would be without the baffle plate. Also, the plasma containment plate separating the plasma containment chamber from the secondary chamber is preferably grounded.
In still another embodiment, the module further includes an additional feed gas port. The additional feed gas port is positioned such that additional feed gases may be injected into the plasma processing module without having the additional feed gases flow through the plasma containment chamber. In one version of this embodiment, the additional feed gas port is connected to the secondary chamber such that additional feed gases may be injected into the secondary chamber without passing through the plasma containment chamber.
In one embodiment, the plasma processing module includes an RF power supply for powering the inductively coupled source of the module. Additionally, the module may further include a biasing arrangement connected to the chuck in the secondary chamber. This biasing arrangement is configured to apply a bias capable of inducing a plasma within the secondary chamber. In one version of this embodiment, the biasing arrangement is configured to apply a soft bias capable of inducing a plasma having a plasma density of no more than about 108 ions/cm3. In one specific example, the biasing arrangement includes an RF power supply for applying the bias.
The various embodiments of the plasma processing module of the present invention may be used in a variety of methods of processing a substrate within a plasma processing module. In one embodiment, a substrate is placed within the secondary chamber of the processing module. A feed gas is then caused to be fed into the plasma containment chamber through the feed gas inlet port. A plasma is energized within the plasma containment chamber using an inductively coupled source to energize the feed gas within the plasma containment chamber. The gases are drawn through the plasma processing module by exhausting the gases from the secondary chamber through the exhaust port. These gases are used to perform certain processes on the substrate.
In one embodiment of a method of the invention, the process of the method is a stripping process for stripping a resist layer from the substrate. In one version of this method, the step of feeding a feed gas into the plasma processing chamber includes the step of feeding O2 and H2O vapor into the plasma processing chamber.
In another embodiment of a method of the invention, a plasma processing module that includes the biasing arrangement connected to the chuck in the secondary chamber is used. The plasma processing module also includes an additional feed gas port positioned such that additional feed gases may be injected into the plasma processing module without having the additional feed gases flow through the plasma containment chamber. The process of this method is a stripping process for stripping a resist layer and various residues from the substrate. In this embodiment, an additional fluorine containing feed gas is injected into the plasma processing module through the additional feed gas port. Also, a soft bias is applied to the chuck such that a plasma is induced within the secondary chamber. In one version of this embodiment, a bias of between about 20-500 W, and preferably 20-200 W for a 200 mm substrate (about 0.6 to about 0.65 W/cm2) is applied thereby inducing a plasma having a plasma density of preferably no more than about 108 ions/cm3 and at most about 109 ions/cm3.